drm/msm: Don't overwrite hw fence in hw_init

Prior to the last commit, this could result in setting the GPU
written fence value back to an older value, if we had missed
updating completed_fence prior to suspend.  This was mostly
harmless as the GPU would eventually overwrite it again with
the correct value.  But we should just not do this.  Instead
just leave a sanity check that the fence looks plausible (in
case the GPU scribbled on memory).

Reported-by: Steev Klimaszewski <steev@kali.org>
Fixes: 95d1deb ("drm/msm/gem: Add fenced vma unpin")
Signed-off-by: Rob Clark <robdclark@chromium.org>
Tested-by: Steev Klimaszewski <steev@kali.org>
Patchwork: https://patchwork.freedesktop.org/patch/490138/
Link: https://lore.kernel.org/r/20220618161120.3451993-2-robdclark@gmail.com

drivers/gpu/drm/msm/adreno/adreno_gpu.c

@@ -498,10 +498,15 @@ int adreno_hw_init(struct msm_gpu *gpu)
 
 		ring->cur = ring->start;
 		ring->next = ring->start;
-
-		/* reset completed fence seqno: */
-		ring->memptrs->fence = ring->fctx->completed_fence;
 		ring->memptrs->rptr = 0;
+
+		/* Detect and clean up an impossible fence, ie. if GPU managed
+		 * to scribble something invalid, we don't want that to confuse
+		 * us into mistakingly believing that submits have completed.
+		 */
+		if (fence_before(ring->fctx->last_fence, ring->memptrs->fence)) {
+			ring->memptrs->fence = ring->fctx->last_fence;
+		}
 	}
 
 	return 0;

drivers/gpu/drm/msm/msm_gpu.c

@@ -418,7 +418,7 @@ static void recover_worker(struct kthread_work *work)
 		 * one more to clear the faulting submit
 		 */
 		if (ring == cur_ring)
-			fence++;
+			ring->memptrs->fence = ++fence;
 
 		msm_update_fence(ring->fctx, fence);
 	}